Effect of individual ankle taping components on the restriction of ankle external inversion moment.

The efficacy of individual taping components to restrain ankle inversion sprain has not been fully understood to date. We aimed to clarify specific taping components that can effectively restrain the amount of angular impulse due to external ankle inversion moments during dynamic ankle motion. Nine participants with chronic ankle instability performed a side-jump with five taping conditions: stirrup, figure eight, heel lock, basketweave, and without taping (control). During the initial landing phase, angular impulses, plantar inclination angle of the whole foot, and plantar flexion angle of the midfoot and hindfoot were compared among these conditions. The basketweave was the only taping condition succeeded in significantly reducing plantar inclination angle of the whole foot, thereby inducing significantly reduced angular impulse due to external ankle inversion moment compared with the control. Although the stirrup and figure eight were found to significantly restrict the plantar flexion angle of the hindfoot and the midfoot, respectively, neither of these components could alter the plantar inclination angle of the whole foot. It was suggested that all the taping components are necessary to reduce the external ankle inversion moments. Certain components should not be used individually to alter the plantar inclination angle of the whole foot.

Mechanical factors affecting the foot eversion moment during the stance phase of running in non-rearfoot strikers.

This study aimed to identify the primary factors that induce rearfoot external eversion moments due to ground reaction force (GRF) in non-rearfoot strikers. The data were compared with those of rearfoot strikers. Totally, 11 healthy males who were habitually non-rearfoot strikers ran barefoot. Rearfoot external eversion/inversion moments due to GRF (Mtot) were decomposed into two components based on mediolateral (Mxy) and vertical (Mz) GRFs. The height of the ankle joint centre and the mediolateral distance from the centre of pressure (COP) to the ankle joint centre (a_cop) were calculated as the lever arms to the Mxy and Mz components. Just after foot contact, non-rearfoot strikers demonstrated a significantly larger Mz, which was strongly dependent on a_cop and produced most of the Mtot, whereas Mxy dominated Mtot in rearfoot strikers. During the consecutive loading phase, non-rearfoot strikers demonstrated a significantly larger Mxy, which was strongly dependent on the mediolateral GRF and substantially contributed to Mtot, unlike the rearfoot strikers, whose Mtot was almost dominated by Mz during the loading phase. It was found that since the factor of generating the moment differs depending on the foot contact pattern, the strategies for suppressing the moment may be different for each foot contact pattern.

Major factors influencing rearfoot external eversion moment during barefoot walking.

BACKGROUND: Excessive rearfoot eversion motion during walking has been considered as a risk factor for lower limb chronic injuries. External moment due to ground reaction force (GRF) is the essential cause by which the rearfoot is passively everted during walking. RESEARCH QUESTION: This study aims to identify the key factors influencing the rearfoot external eversion moments due to the GRF during walking. METHODS: From 3-D foot coordinates and GRF data of 29 healthy participants during walking, the rearfoot external eversion moments due to the GRF and factors composing the moment (height of the ankle joint center, mediolateral GRF, mediolateral distance of the center of pressure relative to the ankle joint center in the transverse plane, vertical GRF) were computed. RESULTS: The mediolateral GRF was a key factor influencing the magnitude of the rearfoot external eversion moment just after foot contact, with which pre-contact medial foot velocity was significantly correlated. During the subsequent support phase, the mediolateral distance of the center of pressure (the application point of the vertical GRF) relative to the ankle joint center was also found to be another determinant of the magnitude of the rearfoot external eversion moment. SIGNIFICANCE: We succeeded in demonstrating the specific factors that most likely explain the magnitude of the rearfoot external eversion moment during initial contact and the subsequent support phase during walking. Based on the findings, specific measures to suppress the rearfoot external eversion moment could be proposed.

Ankle taping can reduce external ankle joint moments during drop landings on a tilted surface.

Ankle taping is commonly used to prevent ankle sprains. However, kinematic assessments investigating the biomechanical effects of ankle taping have provided inconclusive results. This study aimed to determine the effect of ankle taping on the external ankle joint moments during a drop landing on a tilted surface at 25°. Twenty-five participants performed landings on a tilted force platform that caused ankle inversion with and without ankle taping. Landing kinematics were captured using a motion capture system. External ankle inversion moment, the angular impulse due to the medio-lateral and vertical components of ground reaction force (GRF) and their moment arm lengths about the ankle joint were analysed. The foot plantar inclination relative to the ground was assessed. In the taping condition, the foot plantar inclination and ankle inversion angular impulse were reduced significantly compared to that of the control. The only component of the external inversion moment to change significantly in the taped condition was a shortened medio-lateral GRF moment arm length. It can be assumed that the ankle taping altered the foot plantar inclination relative to the ground, thereby shortening the moment arm of medio-lateral GRF that resulted in the reduced ankle inversion angular impulse.

Novel mathematical model to estimate ball impact force in soccer.

To assess ball impact force during soccer kicking is important to quantify from both performance and chronic injury prevention perspectives. We aimed to verify the appropriateness of previous models used to estimate ball impact force and to propose an improved model to better capture the time history of ball impact force. A soccer ball was fired directly onto a force platform (10 kHz) at five realistic kicking ball velocities and ball behaviour was captured by a high-speed camera (5,000 Hz). The time history of ball impact force was estimated using three existing models and two new models. A new mathematical model that took into account a rapid change in ball surface area and heterogeneous ball deformation showed a distinctive advantage to estimate the peak forces and its occurrence times and to reproduce time history of ball impact forces more precisely, thereby reinforcing the possible mechanics of 'footballer's ankle'. Ball impact time was also systematically shortened when ball velocity increases in contrast to practical understanding for producing faster ball velocity, however, the aspect of ball contact time must be considered carefully from practical point of view.

Primary mechanical factors contributing to foot eversion moment during the stance phase of running.

Rearfoot external eversion moments due to ground reaction forces (GRF) during running have been suggested to contribute to overuse running injuries. This study aimed to identify primary factors inducing these rearfoot external eversion moments. Fourteen healthy men ran barefoot across a force plate embedded in the middle of 30-m runway with 3.30 ± 0.17 m · s-1. Total rearfoot external eversion/inversion moments (Mtot) were broken down into the component Mxy due to medio-lateral GRF (Fxy) and the component Mz due to vertical GRF (Fz). Ankle joint centre height and medio-lateral distance from the centre of pressure to the ankle joint centre (a_cop) were calculated as the moment arm of these moments. Mxy dominated Mtot just after heel contact, with the magnitude strongly dependent on Fxy, which was most likely caused by the medio-lateral foot velocity before heel contact. Mz then became the main generator of Mtot throughout the first half of the stance phase, during which a_cop was the critical factor influencing the magnitude. Medio-lateral foot velocity before heel contact and medio-lateral distance from the centre of pressure to the ankle joint centre throughout the first half of the stance phase were identified as primary factors inducing the rearfoot external eversion moment.

A quantitative evaluation of the high elbow technique in front crawl.

Many coaches often instruct swimmers to keep the elbow in a high position (high elbow position) during early phase of the underwater stroke motion (pull phase) in front crawl, however, the high elbow position has never been quantitatively evaluated. The aims of this study were (1) to quantitatively evaluate the "high elbow" position, (2) to clarify the relationship between the high elbow position and required upper limb configuration and (3) to examine the efficacy of high elbow position on the resultant swimming velocity. Sixteen highly skilled and 6 novice male swimmers performed 25 m front crawl with maximal effort and their 3-dimensional arm stroke motion was captured at 60 Hz. An attempt was made to develop a new index to evaluate the high elbow position (Ihe: high elbow index) using 3-dimensional coordinates of the shoulder, elbow and wrist joints. Ihe of skilled swimmers moderately correlated with the average shoulder internal rotation angle (r = -0.652, P < 0.01) and swimming velocity (r = -0.683, P < 0.01) during the pull phase. These results indicate that Ihe is a useful index for evaluating high elbow arm stroke technique during the pull phase in front crawl.

Key motion characteristics of side-step movements in hip-hop dance and their effect on the evaluation by judges.

In hip-hop dance, the elements of motion that discriminate the skill levels of dancers and that influence the evaluations by judges have not been clearly identified. This study set out to extract these motion characteristics from the side-step movements of hip-hop dancing. Eight expert and eight non-expert dancers performed side-step movements, which were recorded using a motion capture system. Nine experienced judges evaluated the dancers' performances. Several parameters, including the range of motion (ROM) of the joint angles (neck, trunk, hip, knee, and face inclination) and phase delays between these angular motions were calculated. A quarter-cycle phase delay between the neck motion and other body parts, seen only in the expert dancers, is highlighted as an element that can distinguish dancers' skill levels. This feature of the expert dancers resulted in a larger ROM during the face inclination than that for the non-expert dancers. In addition, the experts exhibited a bottom-to-top segmental sequence in the horizontal direction while the non-experts did not demonstrate any such sequential motion. Of these kinematic parameters, only the ROM of the face inclination was highly correlated to the judging score and is regarded as being the most appealing element of the side-step movement.

Kinematic analysis of basic rhythmic movements of hip-hop dance: motion characteristics common to expert dancers.

In hip-hop dance contests, a procedure for evaluating performances has not been clearly defined, and objective criteria for evaluation are necessary. It is assumed that most hip-hop dance techniques have common motion characteristics by which judges determine the dancer's skill level. This study aimed to extract motion characteristics that may be linked to higher evaluations by judges. Ten expert and 12 nonexpert dancers performed basic rhythmic movements at a rate of 100 beats per minute. Their movements were captured using a motion capture system, and eight judges evaluated the performances. Four kinematic parameters, including the amplitude of the body motions and the phase delay, which indicates the phase difference between two joint angles, were calculated. The two groups showed no significant differences in terms of the amplitudes of the body motions. In contrast, the phase delay between the head motion and the other body parts' motions of expert dancers who received higher scores from the judges, which was approximately a quarter cycle, produced a loop-shaped motion of the head. It is suggested that this slight phase delay was related to the judges' evaluations and that these findings may help in constructing an objective evaluation system.

Key features of hip hop dance motions affect evaluation by judges.

The evaluation of hip hop dancers presently lacks clearly defined criteria and is often dependent on the subjective impressions of judges. Our study objective was to extract hidden motion characteristics that could potentially distinguish the skill levels of hip hop dancers and to examine the relationship between performance kinematics and judging scores. Eleven expert, six nonexpert, and nine novice dancers participated in the study, where each performed the "wave" motion as an experimental task. The movements of their upper extremities were captured by a motion capture system, and several kinematic parameters including the propagation velocity of the wave were calculated. Twelve judges evaluated the performances of the dancers, and we compared the kinematic parameters of the three groups and examined the relationship between the judging scores and the kinematic parameters. We found the coefficient of variation of the propagation velocity to be significantly different among the groups (P < .01) and highly correlated with the judging scores (r = -0.800, P < .01). This revealed that the variation of propagation velocity was the most dominant variable representing the skill level of the dancers and that the smooth propagation of the wave was most closely related to the evaluation by judges.

Dynamics of the support leg in soccer instep kicking.

We aimed to illustrate support leg dynamics during instep kicking to evaluate the role of the support leg action in performance. Twelve male soccer players performed maximal instep kicks. Their motions and ground reaction forces were recorded by a motion capture system and a force platform. Moments and angular velocities of the support leg and pelvis were computed using inverse dynamics. In most joints of the support leg, the moments were not associated with or counteracting the joint motions except for the knee joint. It can be interpreted that the initial knee flexion motion counteracting the extension joint moment has a role to attenuate the shock of landing and the following knee extension motion associated with the extension joint moment indirectly contributes to accelerate the swing of kicking leg. Also, appreciable horizontal rotation of the pelvis coincided with increase of the interaction moment due to the hip joint reaction force on the support leg side. It can be assumed that the interaction moment was the main factor causing the pelvis counter-clockwise rotation within the horizontal plane from the overhead view that precedes a proximal-to-distal sequence of segmental action of the swing leg.

Ball impact dynamics of instep soccer kicking.

PURPOSE: The purpose of this study was to reveal the foot-ball interaction during ball impact phase of soccer instep kicking. METHODS: Eleven soccer players performed maximal instep kicks. The behavior of kicking foot and ball during ball impact was captured using two ultrahigh-speed cameras at 5000 Hz. Foot motion was described three dimensionally, and the motion of the center of gravity of the ball (CGB) was estimated by the spherical shell model in which the ball deformation was taken into account. The peak ball reaction force acting on the foot was estimated from Newton's equation of motion in which the peak CGB acceleration in sagittal plane was calculated from its velocity slope near the peak ball deformation. RESULTS: During ball impact (9.0 +/- 0.4 ms), the foot was passively abducted and everted. Moreover, an unknown feature--slight dorsal flexion before distinctive plantarflexion--was quantified in most trials. The CGB velocity exceeded that of the foot when the ball was maximally deformed (6.2 +/- 0.6 cm). The magnitude of peak ball reaction force reached 2926 +/- 509 N, which corresponds to approximately twice as that of the mean force (1403 +/- 129 N). From the changes of the foot velocity, the CGB velocity, and the ball deformation, the ball impact phase can be divided into four phases. CONCLUSIONS: The ultrahigh-speed video and methodology in this study documented complex three-dimensional foot motions to impact in soccer instep kicks, dynamic foot-ball interaction, and larger peak ball reaction force on the foot that previously estimated. It can be considered that effectual duration to accelerate the ball is roughly three fourths of visually determined ball contact time.

The effect of fatigue on the underwater arm stroke motion in the 100-m front crawl.

The purpose of this study was to indicate the effect of fatigue on the underwater right arm stroke motion during the 100-m front crawl. The arm stroke motions of eight male competitive swimmers were captured three-dimensionally at 60 Hz in the positions of 15 m and 65 m from the start. The hand velocity, the arm angular velocities and the relative contribution of the arm angular velocities to the hand velocity were computed at each instant during the arm stroke motion. A significant decrease of the hand velocity and the peak angular velocity of shoulder adduction were observed in the second half than in the first half. The contribution of shoulder adduction was especially large in the pull phase and subsequently that of shoulder horizontal abduction became dominant in the push phase. However, in the second half, the contribution of shoulder adduction tended to decrease while that of shoulder internal rotation tended to increase. Thus, it is quite likely that the arm stroke motion of swimmers were driven to be influenced by induced fatigue and resulted in an increase in the contribution of shoulder internal rotation to compensate the decreased contribution of shoulder adduction angular velocity.

Muscle cross-sectional areas and performance power of limbs and trunk in the rowing motion.

Although it is clear that rowers have a large muscle mass, their distribution of muscle mass and which of the main motions in rowing mediates muscle hypertrophy in each body part are unclear. We examine the relationships between partial motion power in rowing and muscle cross-sectional area of the thigh, lower back, and upper arms. Sixty young rowers (39 males and 21 females) participated in the study. Joint positions and forces were measured by video cameras and rowing ergometer software, respectively. One-dimensional motion analysis was performed to calculate the power of leg drive, trunk swing, and arm pull motions. Muscle cross-sectional areas were measured using magnetic resonance imaging. Multiple regression analyses were carried out to determine the association of different muscle cross-sectional areas with partial motion power. The anterior thigh best explained the power demonstrated by leg drive (r2 = 0.508), the posterior thigh and lower back combined best explained the power demonstrated by the trunk swing (r2 = 0.493), and the elbow extensors best explained the power demonstrated by the arm pull (r2 = 0.195). Other correlations, such as arm muscles with leg drive power (r2 = 0.424) and anterior thigh with trunk swing power (r2 = 0.33 5), were also significant. All muscle cross-sectional areas were associated with rowing performance either through the production of power or by transmitting work. The results imply that rowing motion requires a well-balanced distribution of muscle mass throughout the body.

The continuous measurement of the springboard reaction force in gymnastic vaulting.

A new method was established for the continuous measurement of force applied from a springboard to a gymnast in vaulting (board reaction force). Male gymnasts performed a handspring vault using a springboard mounted on force platforms. A high-speed video camera sampled the springboard motion at 500 Hz. The springboard was initially partitioned into 29 segments. The force due to the accelerative motion of the springboard was determined by summing the forces of the individual segments. The board reaction force acting on the gymnast was calculated by subtracting the force due to the accelerative motion of the springboard and weight from the force recorded by the force platform. The new method succeeded in illustrating transient changes of the board reaction force. The horizontal and vertical components of the peak values of the board reaction force were three and two times greater respectively than the average values. A series of tests was conducted to determine whether the number of segments of the springboard model could be reduced without affecting accuracy. A model consisting of only four segments produced almost the same accuracy as the 29-segment model. The simplified model is recommended as a more efficient method to measure board reaction force.

The effect of muscle fatigue on instep kicking kinetics and kinematics in association football.

The aim of this study was to examine the effect of leg muscle fatigue on the kinetics and kinematics of the instep football kick. Fatigue was induced by repeated, loaded knee extension (40% body weight) and flexion (50% body weight) motions on a weight-training machine until exhaustion. The kicking motions of seven male players were captured three-dimensionally at 500 Hz before and immediately after the fatigue protocol. The significantly slower ball velocity observed in the fatigue condition was due to both reduced lower leg swing speed and poorer ball contact. The reduced leg swing speed, represented by a slower toe linear velocity immediately before ball impact and slower peak lower leg angular velocity, was most likely due to a significantly reduced resultant joint moment and motion-dependent interactive moment during kicking. These results suggest that the specific muscle fatigue induced in the present study not only diminished the ability to generate force, but also disturbed the effective action of the interactive moment leading to poorer inter-segmental coordination during kicking. Moreover, fatigue obscured the eccentric action of the knee flexors immediately before ball impact. This might increase the susceptibility to injury.

Segmental dynamics of soccer instep kicking with the preferred and non-preferred leg.

Detailed time-series of the resultant joint moments and segmental interactions during soccer instep kicking were compared between the preferred and non-preferred kicking leg. The kicking motions of both legs were captured for five highly skilled players using a three-dimensional cinematographic technique at 200 Hz. The resultant joint moment (muscle moment) and moment due to segmental interactions (interaction moment) were computed using a two-link kinetic chain model composed of the thigh and lower leg (including shank and foot). The mechanical functioning of the muscle and interaction moments during kicking were clearly illustrated. Significantly greater ball velocity (32.1 vs. 27.1 m . s(-1)), shank angular velocity (39.4 vs. 31.8 rad . s(-1)) and final foot velocity (22.7 vs. 19.6 m . s(-1)) were observed for the preferred leg. The preferred leg showed a significantly greater knee muscle moment (129.9 N . m) than the non-preferred leg (93.5 N . m), while no substantial differences were found for the interaction moment between the two legs (79.3 vs. 55.7 N . m). These results indicate that the highly skilled soccer players achieved a well-coordinated inter-segmental motion for both the preferred and non-preferred leg. The faster leg swing observed for the preferred leg was most likely the result of the larger muscle moment.

Three-dimensional kinetic analysis of side-foot and instep soccer kicks.

PURPOSE: The purpose of this study was to identify the kinetic aspects of side-foot and instep soccer kicks to understand the different mechanics underlying the two kicks. METHODS: The motions of both kicks were captured using a three-dimensional cinematographic technique. The kicking leg was modeled as a three-link kinetic chain composed of thigh, shank, and foot, from which joint torques and angular velocities were computed. RESULTS: The ball velocity of the side-foot kick (23.4 +/- 1.7 m x s(-1)) was significantly slower than that of the instep kick (28.0 +/- 2.1 m.s(-1)). Significant differences were also observed between the two kicks for the magnitude of hip external rotation torque (56 +/- 12 N.m in the side-foot kick; 33 +/- 8 N.m in the instep kick) and hip external rotation angular velocity (11.1 +/- 2.4 rad x s(-1) in the side-foot kick; 6.0 +/- 2.0 rad x s(-1) in the instep kick). CONCLUSION: These results indicated that to hit the ball with the medial side of the foot, a complicated series of rotational motions are required for the side-foot kick. The hip external rotation torque dominantly exhibited in the side-foot kick caused the clockwise rotation of the thigh-shank plane at the later stage of kicking. This may allow the hip external rotation motion to increase directly the forward velocity of the side foot, with which players can squarely impact the ball.